Integrated Circuit with Sidewall Spacers for Gate Spacers

ABSTRACT

Various examples of an integrated circuit with a sidewall spacer and a technique for forming an integrated circuit with such a spacer are disclosed herein. In some examples, the method includes receiving a workpiece that includes a substrate and a gate stack disposed upon the substrate. A spacer is formed on a side surface of the gate stack that includes a spacer layer with a low-k dielectric material. A source/drain region is formed in the substrate; and a source/drain contact is formed coupled to the source/drain region such that the spacer layer of the spacer is disposed between the source/drain contact and the gate stack.

PRIORITY DATA

The present application is a continuation application of U.S.application Ser. No. 16/678,472, filed Nov. 8, 2019, which is divisionalapplication of U.S. application Ser. No. 15/813,742, filed Nov. 15,2017, each of which is incorporated herein by reference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. In the course of IC evolution, functional density (i.e., thenumber of interconnected devices per chip area) has generally increasedwhile geometry size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling downprocess generally provides benefits by increasing production efficiencyand lowering associated costs. However, such scaling down has also beenaccompanied by increased complexity in design and manufacturing ofdevices incorporating these ICs. Parallel advances in manufacturing haveallowed increasingly complex designs to be fabricated with precision andreliability.

For example, fabrication advances have reduced not only the size of thecircuit features but the spacing between the features. However, evenwhen such circuits can be fabricated, other issues may arise due to thereduced space between features. As merely one example, circuit featuresin close proximity may exhibit electrical effects on one another, suchas capacitance and noise, which are exacerbated as the spacing isreduced. Low power devices may demonstrate increased sensitivity to sucheffects, which in turn, may limit minimum power and maximum performance.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A and 1B are flow diagrams of a method of forming an integratedcircuit according to various aspects of the present disclosure.

FIGS. 2-13B are cross-sectional diagrams of a portion of a workpieceundergoing the method of forming an integrated circuit according tovarious aspects of the present disclosure.

FIGS. 14A and 14B are flow diagrams of a method of forming an integratedcircuit with a doped spacer layer according to various aspects of thepresent disclosure.

FIGS. 15-22B are cross-sectional diagrams of a portion of a workpieceundergoing the method of forming an integrated circuit with a dopedspacer layer according to various aspects of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations beyond the extentnoted.

Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “over,” “below,” “beneath,”“up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for easeof the present disclosure of one features relationship to anotherfeature. The spatially relative terms are intended to cover differentorientations of the device including the features.

In the pursuit of smaller and more energy-efficient integrated circuits,features are being fabricated in closer proximity. As the spacingbetween features is reduced, adverse electrical effects, such asparasitic capacitance between the features, become more pronounced.Furthermore, individual devices may become more sensitive to theseeffects.

One example of parasitic capacitance occurs between a gate stack of atransistor (e.g., a CMOS transistor) and an adjacent source/draincontact. The capacitive coupling may delay the rise and fall of voltageat the gate and at the source/drain contact. Previously, the effect wassmall enough that this capacitance was considered negligible. However asdevice size shrinks, the distance between the gate and the source/draincontact is also reduced, which may increase the magnitude of thecapacitance. Likewise, as the operational voltages of the transistor andother device are reduced, the sensitivity to parasitic capacitancesincreases. Accordingly, the previously negligible gate-contactcapacitance may now decrease switching speed, increase switching powerconsumption, and increase coupling noise. In the interest of alleviatingthese effects, the present disclosure provides some examples of a devicewith reduced gate-contact capacitance and a technique for fabricatingthe device.

In some embodiments, the technique forms a sidewall spacer disposedbetween the gate stack and any source/drain contact. The sidewall spacermay have multiple layers, such as a dielectric hard mask layer disposedproximate to the gate stack and a spacer layer disposed on thedielectric hard mask layer. In some such examples, the sidewalldielectric includes a porous low-k dielectric material. The porous low-kdielectric material may be formed by depositing a low-k precursor and aporogen and subsequently curing the precursor during a gate-replacementprocess. Curing the precursor causes the porogen to create voids in thespacer layer material that reduce the dielectric constant. Due in partto the reduced dielectric constant, the resulting spacer layer reducesthe capacitive coupling between the gate stack and the source/draincontact.

In further embodiments, the technique forms a sidewall spacer with adielectric hard mask layer disposed proximate to the gate stack and adoped spacer layer disposed on the dielectric hard mask layer. The dopedspacer layer may include dopants such as boron or phosphorus. Thedopants act to reduce the dielectric constant of the doped spacer layerand, by extension, reduce the capacitive coupling between the gate stackand the source/drain contact.

In these examples and others, the sidewall spacer has a reduceddielectric constant compared to a conventional spacer. In turn, thereduced dielectric constant may reduce the capacitance between the gateand the source/drain contact. The lower capacitance may increase deviceswitching speed, reduce switching power, reduce parasitic power loss,and, in some examples, may avoid transient events, such as logicglitches caused by irregularities in switching behavior. However, unlessotherwise noted, no embodiment is required to provide any particularadvantage.

Examples of the technique and the resulting structure are described withreference to FIGS. 1A-13B. In particular, FIGS. 1A and 1B are flowdiagrams of a method 100 of forming an integrated circuit according tovarious aspects of the present disclosure. Additional steps can beprovided before, during, and after the method 100, and some of the stepsdescribed can be replaced or eliminated for other examples of the method100. FIGS. 2-13B are cross-sectional diagrams of a portion of aworkpiece 200 undergoing the method of forming an integrated circuitaccording to various aspects of the present disclosure. FIGS. 2-13B havebeen simplified for the sake of clarity and to better illustrate theconcepts of the present disclosure. Additional features may beincorporated into the workpiece 200, and some of the features describedbelow may be replaced or eliminated for other examples of the workpiece200.

Referring to block 102 of FIG. 1A and to FIG. 2, the workpiece 200 isreceived. The workpiece 200 includes a substrate 202, which may have oneor more features formed upon it. In various embodiments, the substrate202 includes an elementary (single element) semiconductor, such assilicon or germanium in a crystalline structure; a compoundsemiconductor, such as silicon germanium, silicon carbide, galliumarsenic, gallium phosphide, indium phosphide, indium arsenide, and/orindium antimonide; a non-semiconductor material, such as soda-limeglass, fused silica, fused quartz, and/or calcium fluoride (CaF₂);and/or combinations thereof.

The substrate 202 may be uniform in composition or may include variouslayers. The layers may have similar or different compositions. Forexample, a silicon-on-insulator (SOI) substrate 202 includes aninsulator layer, such as a semiconductor oxide, a semiconductor nitride,a semiconductor oxynitride, a semiconductor carbide, and/or othersuitable insulator materials for electrical isolation. In furtherexamples, the substrate 202 includes layers with different semiconductorlattice arrangements to induce device strain and thereby tune deviceperformance.

Some elements of an integrated circuit device may already be formed onthe substrate 202 when it is received in block 102. For example, theworkpiece 200 may have a gate stack 204 disposed on the substrate 202.The gate stack 204 may include an interfacial layer 206 where it meetsthe substrate 202. The interfacial layer 206 may include an interfacialmaterial, such as a semiconductor oxide, semiconductor nitride,semiconductor oxynitride, other semiconductor dielectrics, othersuitable interfacial materials, and/or combinations thereof. Theinterfacial layer 206 may be formed to any suitable thickness using anysuitable process including thermal growth, atomic layer deposition(ALD), chemical vapor deposition (CVD), high-density plasma CVD(HDP-CVD), physical vapor deposition (PVD), spin-on deposition, and/orother suitable deposition processes.

The gate stack 204 may also include a gate dielectric 208 disposed onthe interfacial layer 206. The gate dielectric 208 may include one ormore dielectric materials, which are commonly characterized by theirdielectric constant relative to silicon dioxide. In some embodiments,the gate dielectric 208 includes a high-k dielectric material, such asHfO₂, HfSiO, HfSiON, HfTaO, HfTiO, HfZrO, zirconium oxide, aluminumoxide, hafnium dioxide-alumina (HfO₂—Al₂O₃) alloy, other suitable high-kdielectric materials, and/or combinations thereof. Additionally or inthe alternative, the gate dielectric 208 may include other dielectrics,such as a semiconductor oxide, semiconductor nitride, semiconductoroxynitride, semiconductor carbide, amorphous carbon,tetraethylorthosilicate (TEOS), other suitable dielectric material,and/or combinations thereof. The gate dielectric 208 may be formed toany suitable thickness using any suitable process including ALD, CVD,HDP-CVD, PVD, spin-on deposition, and/or other suitable depositionprocesses.

In some embodiments, the gate stack 204 includes a gate electrode 210disposed on the gate dielectric 208. It is noted that the gate electrode210, gate dielectric 208 and/or interfacial layer 206 may beplaceholders. For example in a gate-last process, a temporary gateelectrode material is used as a placeholder during some of thefabrication processes. The temporary gate electrode material issubsequently removed and replaced with a functional gate electrodematerial, such as metal. This may be done when the functional material(e.g., gate electrode material, gate dielectric layer material,interfacial layer, etc.) is sensitive to some fabrication processes,such as annealing. Accordingly when the workpiece 200 is received, thegate electrode 210 may be a placeholder gate electrode or a functionalgate electrode. A placeholder gate electrode 210 may includepolysilicon, dielectric material, and/or other suitable materials. Incontrast, a functional gate electrode 210 may include tungsten,aluminum, copper, titanium, tantalum, molybdenum, ruthenium, tantalumnitride, nickel silicide, cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN,TaC, TaSiN, metal alloy, polysilicon, other suitable materials, and/orcombinations thereof.

The workpiece 200 may also include one or more masking layers disposedon the gate electrode 210. In the illustrated embodiments, the workpiece200 includes a first hard mask layer 212 and a second hard mask layer214 disposed on the gate electrode 210. Each of the first hard masklayer 212 and second hard mask layer 214 may include any suitablemasking material, such as: a dielectric material (e.g., a semiconductoroxide, a semiconductor nitride, a semiconductor oxynitride, asemiconductor carbide, a semiconductor oxycarbonitride, etc.),polysilicon, Spin-On Glass (SOG), TEOS, Plasma Enhanced CVD oxide(PE-oxide), High-Aspect-Ratio-Process (HARP)-formed oxide, and/or othersuitable materials. The first hard mask layer 212 and second hard masklayer 214 may be formed to any suitable thickness using any suitableprocess including ALD, CVD, HDP-CVD, PVD, spin-on deposition, and/orother suitable deposition processes. In an embodiment, the first hardmask layer 212 includes silicon oxycarbonitride, and the second hardmask layer 214 includes polysilicon. While the first hard mask layer 212and the second hard mask layer 214 may have any suitable thickness andshape, in some examples, the second hard mask layer 214 has a roundedprofile due to various fabrication processes, such as etching a layer ofgate electrode 210 material and/or gate dielectric 208 material todefine the gate stack 204.

Referring to block 104 of FIG. 1A and to FIG. 3, an inner spacer layer302 is formed on the workpiece 200. The inner spacer layer 302 may beformed on exposed portions of the substrate 202 as well as on the gatestack 204. In particular, the inner spacer layer 302 may be formed onthe vertical side surfaces of the gate stack 204 (i.e., on the verticalside surfaces of the interfacial layer 206, gate dielectric 208, and/orgate electrode 210). In this way, the inner spacer layer 302 begins todefine a sidewall spacer 304 of the gate stack 204.

The inner spacer layer 302 may include any suitable masking material,such as: a dielectric material (e.g., a semiconductor oxide, asemiconductor nitride, a semiconductor oxynitride, a semiconductorcarbide, a semiconductor oxycarbonitride, etc.), polysilicon, SOG, TEOS,PE-oxide, HARP-formed oxide, and/or other suitable material. In one suchembodiment, the inner spacer layer 302 includes silicon oxycarbonitride.The inner spacer layer 302 may be formed to any suitable thickness usingany suitable deposition technique (e.g., CVD, HDP-CVD, ALD, etc.). Invarious embodiments, the inner spacer layer 302 has a thickness betweenabout 1 nm and about 10 nm and is deposited by a conformal CVD and/orALD process.

Referring to block 106 of FIG. 1A and to FIG. 4, a low-k precursor 402is formed on the workpiece 200. In that regard, the low-k precursor 402may be formed on the inner spacer layer 302, and in particular, on thevertical side surfaces of the inner spacer layer 302 adjacent the gatestack 204. In this way, the low-k precursor 402 further defines thesidewall spacer 304 of the gate stack 204. Within the sidewall spacer304, a portion of the inner spacer layer 302 separates the low-kprecursor 402 from the substrate 202 in some embodiments. Additionallyor in the alternative, the low-k precursor 402 may contact the substrate202 within the sidewall spacer 304.

The low-k precursor 402 may include one or more precursor materials thatform a low-k dielectric material when processed. Whereas silicon dioxidehas a dielectric constant of about 3.9, in various examples, the low-kprecursor 402 is used to form a material with a dielectric constantbetween about 3.9 and about 1. In some examples, the low-k precursor 402includes a combination of a dielectric precursor (e.g., TEOS,tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMS),methyltriethoxysilane (MTES), diethoxy methyl silane (DEMS), etc.) and aporogen (e.g., α-Terpinene (ATRP), polystyrene, etc.). The low-kprecursor 402 may be formed to any suitable thickness using any suitabledeposition technique (e.g., CVD, HDP-CVD, ALD, etc.). In some examples,the low-k precursor 402 has a thickness between about 1 nm and about 10nm and is deposited by conformal CVD and/or ALD process. Forming thelow-k precursor 402 may include introducing a carbon-based porogen(e.g., CO₂) into the low-k precursor 402 after the precursor isdeposited by exposing the workpiece to a carbon-based plasma.

Referring to block 108 of FIG. 1A and to FIG. 5, an etching process isperformed on the workpiece 200 to create recesses 502 in which to formsource/drain regions. The etching process may be performed using anysuitable etching method, such as wet etching, dry etching, Reactive IonEtching (RIE), ashing, and/or other etching methods and may use anysuitable etchant chemistries, such as carbon tetrafluoride (CF₄),difluoromethane (CH₂F₂), trifluoromethane (CHF₃), other suitableetchants, and/or combinations thereof. The etching methods and theetchant chemistries may vary as the low-k precursor 402, inner spacerlayer 302, and substrate 202 are etched to target the particularmaterial being etched while minimizing unintended etching of thematerials not being targeted. In some such example, the etching processis configured to anisotropically etch the portions of the low-kprecursor 402 and the inner spacer layer 302 located directly on thesubstrate 202, while leaving the portions of the low-k precursor 402 andthe inner spacer layer 302 on the vertical sidewalls of the gate stack204. The etching process may expose some of the second hard mask layer214. However in general, the first hard mask layer 212 and the secondhard mask layer 214 protect the gate stack from the etching process.

Referring to block 110 of FIG. 1A and to FIG. 6, an epitaxy process isperformed on the workpiece 200 to grow source/drain regions 602 withinthe recesses 502. In various examples, the epitaxy process includes aCVD deposition technique (e.g., Vapor-Phase Epitaxy (VPE) and/orUltra-High Vacuum CVD (UHV-CVD)), molecular beam epitaxy, and/or othersuitable processes. The epitaxy process may use gaseous and/or liquidprecursors, which interact with a component of the substrate 202 (e.g.,silicon) to form the source/drain regions 602. The resultantsource/drain regions 602 may be in-situ doped to include p-type dopants,such as boron or BF₂; n-type dopants, such as phosphorus or arsenic;and/or other suitable dopants including combinations thereof.Additionally or in the alternative, the source/drain regions 602 may bedoped using an implantation process (i.e., a junction implant process)after the source/drain regions 602 are formed. Once the dopant(s) areintroduced, a dopant activation processes, such as Rapid ThermalAnnealing (RTA) and/or a laser annealing processes, may be performed toactivate the dopants within the source/drain regions 602 as shown inblock 112 of FIG. 1A.

The source/drain regions 602 may have any suitable shape, and in someexamples, the source/drain regions 602 have a substantially u-shapedprofile where a vertical sidewall portion of each of the source/drainregions 602 indicated by marker 604 is substantially aligned with anouter vertical surface of the low-k precursor 402 (and by extensionaligned with the outer vertical surface of the sidewall spacer 304).Furthermore in some examples, halo/pocket implantation is performed onthe substrate 202, and as a result, the source/drain regions 602 extendunderneath the sidewall spacer 304.

Referring to block 114 of FIG. 1A and to FIG. 7, a Contact Etch StopLayer (CESL) 702 is formed on the workpiece 200. The CESL 702 may beformed on the source/drain regions 602 and on the gate stack 204, and inparticular, on the vertical side surfaces of the low-k precursor 402adjacent the gate stack 204. The CESL 702 may include any suitablematerial, such as: a dielectric material (e.g., a semiconductor oxide, asemiconductor nitride, a semiconductor oxynitride, a semiconductorcarbide, a semiconductor oxycarbonitride, etc.), polysilicon, SOG, TEOS,PE-oxide, HARP-formed oxide, and/or other suitable material. In someexamples, the CESL 702 includes silicon oxycarbonitride. The CESL 702may be formed to any suitable thickness using any suitable depositiontechnique (e.g., CVD, HDP-CVD, ALD, etc.). In some examples, the CESL702 has a thickness between about 1 nm and about 10 nm, and is depositedby a conformal CVD and/or ALD process.

Referring to block 116 of FIG. 1A and referring still to FIG. 7, a firstInter-Level Dielectric (ILD) layer 704 is formed on the workpiece 200.The first ILD layer 704 acts as an insulator that supports and isolatesconductive traces of an electrical multi-level interconnect structurethat electrically interconnects elements of the workpiece 200, such asthe source/drain regions 602 and the gate electrode 210. The first ILDlayer 704 may comprise a dielectric material (e.g., a semiconductoroxide, a semiconductor nitride, a semiconductor oxynitride, asemiconductor carbide, etc.), SOG, fluoride-doped silicate glass (FSG),phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), BlackDiamond® (Applied Materials of Santa Clara, Calif.), Xerogel, Aerogel,amorphous fluorinated carbon, parylene, BCB, SILK® (Dow Chemical ofMidland, Mich.), and/or combinations thereof. The first ILD layer 704may be formed by any suitable process including CVD, PVD, spin-ondeposition, and/or other suitable processes.

Referring to block 118 of FIG. 1B and to FIG. 8, a chemical mechanicalpolish/planarization (CMP) process is performed on the workpiece 200.The CMP process may remove some or all of the first hard mask layer 212and the second hard mask layer 214 from the gate electrode 210, and maybe followed by a hard mask etch back to remove any remaining materialfrom the gate electrode 210. The hard mask etch back process may beperformed using any suitable etching method, such as wet etching, dryetching, RIE, ashing, etc. using any suitable etchant chemistryconfigured to selectively remove the first hard mask layer 212 and/orthe second hard mask layer 214.

Referring to block 120 of FIG. 1B and to FIG. 9, in examples where anycomponents of the gate stack 204 (e.g., the gate electrode 210, the gatedielectric 208, and/or the interfacial layer 206) are placeholders, theplaceholder components are removed as part of a gate replacementprocess. In the illustrated example, at least the gate electrode 210 andthe gate dielectric are removed to provide a recess 902 within the gatestack 204. Removing the placeholder components of the gate stack 204 mayinclude one or more etching processes (e.g., wet etching, dry etching,RIE) using an etchant chemistry configured to selectively etch thematerial of the particular placeholder component being targeted withoutsignificant etching of surrounding materials such as the inner spacerlayer 302, the low-k precursor 402, the first ILD layer 704, the CESL702, etc.

Referring to block 122 of FIG. 1B and referring still to FIG. 9, acuring process is performed on the workpiece 200. The curing process isconfigured to convert the low-k precursor 402 into a low-k spacer layer903. For example, the curing process may drive off a porogen from theprecursor 402 leaving voids 904 (enlarged for clarity) in the low-kspacer layer 903. The voids 904 may reduce the dielectric constant ofthe remaining material of low-k spacer layer 903. The removal of theplaceholder gate electrode 210 may promote the removal of the porogen byallowing it to escape through the sides of the low-k spacer layer 903(through the inner spacer layer 302) by way of the recess 902. In otherexamples, the curing process causes the porogen to organize themolecular structure of the precursor to create voids 904 in low-k spacerlayer 903 without driving off the porogen.

The curing process may utilize any suitable technique. The curingprocess may utilize heat and/or radiation such as ultraviolet radiationto cause a chemical change in the low-k precursor 402 to form the low-kspacer layer 903. In various examples, the workpiece 200 is heated in avacuum or an inert-gas environment to a temperature between about 350°C. and about 450° C. While heated, the workpiece 200 is exposed toradiation having one or more wavelengths between about 150 nm and about250 nm for between about 50 and about 150 seconds. In further examples,curing includes heating at least part of the workpiece 200 to atemperature between about 350° C. and about 450° C. using amicro-annealing process.

After the curing process, the low-k spacer layer 903 may have adielectric constant between about 3.9 and about 1, and in some examples,the low-k spacer layer 903 has a dielectric constant of about 3.

Referring to block 124 of FIG. 1B and to FIG. 10, replacement elementsof the gate stack 204, such as a replacement gate dielectric 1002, areplacement gate electrode 1004, are formed on the workpiece 200 withinthe recess 902. The replacement gate dielectric 1002 and the replacementgate electrode 1004 may be different in composition from the gatedielectric 208 and the gate electrode 210 that was previously removed.For example, the replacement gate dielectric 1002 may include a high-kdielectric material, such as HfO₂, HfSiO, HfSiON, HfTaO, HfTiO, HfZrO,zirconium oxide, aluminum oxide, hafnium dioxide-alumina (HfO₂—Al₂O₃)alloy, other suitable high-k dielectric materials, and/or combinationsthereof. The replacement gate dielectric 1002 may extend horizontallyalong the substrate 202 and vertically along some or all of the innerspacer layer 302. The replacement gate dielectric 1002 may be formed toany suitable thickness using any suitable process including ALD, CVD,HDP-CVD, PVD, spin-on deposition, and/or other suitable depositionprocesses.

Turning to the replacement gate electrode 1004, the gate electrode 1004includes one or more metal-containing layers, such as a capping layer, awork function layer, a barrier layer, and/or an electrode fill. Examplesof these layers are shown and described in more detail below.

Referring to block 126 of FIG. 1B and to FIG. 11, a second ILD layer1102 may be formed on the workpiece 200. Similar to the first ILD layer704, the second ILD layer 1102 acts as an insulator that supports andisolates conductive traces of the multi-level interconnect structure.Also similar to the first ILD layer 704, the second ILD layer 1102 mayinclude any suitable dielectric material and may be formed by anysuitable process including CVD, PVD, spin-on deposition, and/or othersuitable processes.

Referring to block 128 of FIG. 1B and to FIG. 12, contact-open etchingis performed on the workpiece 200 to expose the source/drain regions 602where contacts are to be formed. The contact-open etching may includeforming a photoresist layer 1202 on the workpiece. An exemplaryphotoresist layer 1202 includes a photosensitive material that causesthe layer to undergo a property change when exposed to light. Thisproperty change can be used to selectively remove exposed or unexposedportions of the photoresist layer in a process referred to aslithographic patterning. In one such embodiment, a photolithographicsystem exposes the photoresist layer 1202 to radiation in a particularpattern determined by a mask. Light passing through or reflecting offthe mask strikes the photoresist layer 1202 thereby transferring apattern formed on the mask to the photoresist 1202. In other suchexamples, the photoresist layer 1202 is patterned using a direct writeor maskless lithographic technique, such as laser patterning, e-beampatterning, and/or ion-beam patterning. Once exposed, the photoresistlayer 1202 is developed leaving the exposed portions of the resist, orin alternative examples, leaving the unexposed portions of the resist.An exemplary patterning process includes soft baking of the photoresistlayer 1202, mask aligning, exposure, post-exposure baking, developingthe photoresist layer 1202, rinsing, and drying (e.g., hard baking).

The patterned photoresist layer 1202 exposes portions of the second ILDlayer 1102 to be etched. Accordingly, after patterning the photoresistlayer 1202, one or more etching processes may be performed on theworkpiece 200 to open those portions of the second ILD layer 1102, thefirst ILD layer 704, and the CESL 702 not covered by the photoresistlayer 1202. The etching processes may include any suitable etchingtechnique, such as wet etching, dry etching, RIE, ashing, and/or otheretching methods. In some examples, etching includes multiple etchingsteps with different etching chemistries, each targeting a particularmaterial of the workpiece 200. The contact-open etching of block 128leaves a recess 1204 exposing the source/drain region 602 where acontact is to be formed. The recess 1204 may extend into thesource/drain region 602 to increase the contact surface area between thesource/drain region 602 and the contact.

Referring to block 130 of FIG. 1B and to FIG. 13A, the source/draincontact 1302 is formed on the workpiece 200 within the recess 1204 andis physically and electrically coupled to the source/drain region 602.The contact 1302 may include any suitable conductive material, such asW, Al, Cu, Ti, Ag, Ru, Mo, TiN, WN, TiAl, TiAlN, TaCN, TaC, TaSiN, metalalloy, metal silicide, and/or other suitable materials. The contact 1302material(s) may be deposited using any suitable process, such as CVD,PVD, sputtering, plating, and/or other suitable processes. A CMP processmay be performed after deposition of to remove any excess material on,for example, the second ILD layer 1102.

The contact 1302 may extend between the vertical portions of the CESL702 and the sidewall spacer 304 such that the CESL 702 and the sidewallspacer 304 separate the contact 1302 from the adjacent gate stack(s)204. It has been determined that such an arrangement produces acapacitive coupling between the contact 1302 and the gate stack 204. Insome examples, the resulting capacitance affects the switching speedand/or the threshold voltage of the associated transistor. However, thestructure and composition of the low-k spacer layer 903 may act toreduce this gate-contact capacitance. In particular, the low-kdielectric material of the low-k spacer layer 903 formed by thedeposition of the precursor in block 106 and the curing process of block122 reduces this capacitance compared to other configurations.

Referring now to FIG. 13B, the inner spacer layer 302, the low-k spacerlayer 903, the CESL 702, the gate stack 204, and the surroundingstructures of the workpiece 200 are enlarged for greater detail. Inparticular, individual elements of the replacement gate electrode 1004are shown. As noted above, the replacement gate electrode 1004 mayinclude layers such as a capping layer 1304, a barrier layer 1306, oneor more work function layer(s) 1308, an electrode fill 1310, etc.

Referring first to the capping layer 1304, the capping layer 1304 may bedisposed on the horizontal surfaces of the replacement gate dielectric1002 as well as the vertical surfaces of the replacement gate dielectric1002 that extend vertically along the inner spacer layer 302. Thecapping layer 706 may include any suitable conductive material includingmetals (e.g., W, Al, Ta, Ti, Ni, Cu, Co, etc.), metal nitrides, and/ormetal silicon nitrides, and may be deposited via CVD, ALD, PE CVD,PEALD, PVD, and/or other suitable deposition process. In variousembodiments, the capping layer 1304 includes TaSiN, TaN, or TiN.

A barrier layer 1306 may be disposed on the horizontal and verticalsurfaces of the capping layer 1304. The barrier layer 1306 may containany suitable material, such as W, Ti, TiN, Ru, or combinations thereof.Materials for the barrier layer 1306 may be selected based on theirresilience to diffusion into the capping layer 1304. The barrier layer1306 may be deposited by any suitable technique including ALD, CVD, PECVD, PEALD, PVD (e.g., sputtering), and/or combinations thereof.

One or more work function layer(s) 1308 are disposed on the horizontaland vertical surfaces of the capping layer 1304. Suitable work functionlayer 1308 materials include n-type and/or p-type work functionmaterials based on the type of device to which the gate stack 204corresponds. Exemplary p-type work function metals include TiN, TaN, Ru,Mo, Al, WN, ZrSi₂, MoSi₂, TaSi₂, NiSi₂, WN, other suitable p-type workfunction materials, and/or combinations thereof. Exemplary n-type workfunction metals include Ti, Ag, TaAl, TaAlC, TiAlN, TaC, TaCN, TaSiN,Mn, Zr, other suitable n-type work function materials, and/orcombinations thereof. The work function layer(s) 1308 may be depositedby any suitable technique including ALD, CVD, PE CVD, PEALD, PVD, and/orcombinations thereof.

An electrode fill 1310 is disposed on the work function layer(s) 1308.The electrode fill 1310 may include any suitable material includingmetals (e.g., W, Al, Ta, Ti, Ni, Cu, Co, etc.), metal oxides, metalnitrides and/or combinations thereof, and in an example, the electrodecore includes tungsten (W). The electrode fill 1310 may be deposited byany suitable technique including ALD, CVD, PE CVD, PEALD, PVD, and/orcombinations thereof.

As noted above, in various examples, the inner spacer layer 302 has awidth 1312 between about 1 nm and about 10 nm, the low-k spacer layer903 has a width 1314 between about 1 nm and about 10, and the CESL 702has a width 1316 between about 1 nm and about 10 nm. The height 1318 ofthe gate stack 204 disposed between these layers (and by extension theheight of the inner spacer layer 302 and the CESL 702) is between about15 nm and about 25 nm in various examples. Accordingly a ratio of heightto width for the inner spacer layer 302 and CESL 702 may be betweenabout 1.5:1 and about 25:1. As the inner spacer layer 302 may extendbetween the low-k spacer layer 903 and the substrate 202, the height ofthe low-k spacer layer 903 is between about 5 nm and about 25 nm for acorresponding height-to-width ratio of between 0.5:1 and about 25:1 invarious examples.

Referring to block 132 of FIG. 1B, the workpiece 200 is provided forfurther fabrication.

Further examples of the technique and the resulting structure thatincorporate different compositions for the spacer layer are describedwith reference to FIGS. 14A-22B. In that regard, FIGS. 14A and 14B areflow diagrams of a method 1400 of forming an integrated circuit with adoped spacer layer according to various aspects of the presentdisclosure. Additional steps can be provided before, during, and afterthe method 1400, and some of the steps described can be replaced oreliminated for other examples of the method 1400. FIGS. 15-22B arecross-sectional diagrams of a portion of a workpiece 1500 undergoing themethod of forming an integrated circuit with a doped spacer layeraccording to various aspects of the present disclosure. FIGS. 15-22Bhave been simplified for the sake of clarity and to better illustratethe concepts of the present disclosure. Additional features may beincorporated into the workpiece 1500, and some of the features describedbelow may be replaced or eliminated for other examples of the workpiece1500.

Referring to block 1402 of FIG. 14A and to FIG. 15, the workpiece 1500is received. The workpiece 1500 may be substantially similar toworkpiece 200 and may include a substrate 202, a gate stack 204 (with aninterfacial layer 206, gate dielectric 208, and/or a gate electrode210), a first hard mask layer 212, and/or a second hard mask layer 214,each substantially as described above.

Referring to block 1404 of FIG. 14A and to FIG. 16, an inner spacerlayer 302 is formed on the workpiece 1500. The inner spacer layer 302may be formed on the vertical side surfaces of the gate stack 204 (i.e.,on the vertical side surfaces of the interfacial layer 206, gatedielectric 208, and/or gate electrode 210). The portion of the innerspacer layer 302 on the vertical side surface of a gate stack 204partially defines a sidewall spacer 304 of the gate stack 204.

The inner spacer layer 302 may be substantially as described above incomposition, and in one such example, the inner spacer layer 302includes silicon oxycarbonitride. The inner spacer layer 302 may beformed to any suitable thickness using any suitable deposition technique(e.g., CVD, HDP-CVD, ALD, etc.). In various examples, the inner spacerlayer 302 has a thickness between about 1 nm and about 10 nm and isdeposited by a conformal CVD and/or ALD process.

Referring to block 1406 of FIG. 14A and referring still to FIG. 16, alow-k precursor 1602 is formed on the workpiece 1500. In particular, thelow-k precursor 1602 may be formed on the vertical side surfaces of theinner spacer layer 302 adjacent the gate stack 204. In this way, thelow-k precursor 1602 further defines the sidewall spacer 304 of the gatestack 204.

The low-k precursor 1602 may include any suitable material, and invarious examples, the low-k precursor 1602 includes a dielectricmaterial (e.g., a semiconductor oxide, a semiconductor nitride, asemiconductor oxynitride, a semiconductor carbide, a semiconductoroxycarbonitride) doped with a p-type dopant, such as boron or BF₂, or ann-type dopant, such as phosphorus or arsenic, to modify the dielectricconstant of the dielectric material. The dopant type in the low-kprecursor 1602 may be independent of the dopants in the channel regionand source/drain regions 602 of the transistor, and the low-k precursor1602 may be doped with the same type or the opposite type of the dopantin the source/drain regions 602. In various examples, the low-kprecursor 1602 includes silicon oxide, silicon nitride, and/or siliconoxynitride and is doped with boron and/or phosphorous. The low-kprecursor 1602 may include any suitable concentration of the dopant, andin various examples, the dopant concentration is between about 1×10¹⁶atoms/cm³ and about 1×10²¹ atoms/cm³.

The dopant reduces the capacitive coupling between the gate stack 204and a contact, and to further reduce the capacitive coupling, the dopantmay be introduced into a porous dielectric. In some such examples, thelow-k precursor 1602 includes a low-k dielectric precursor (e.g., TEOS,TMOS, MTMS, MTES, DEMS, etc.) and a porogen (e.g., ATRP, polystyrene,etc.) and a p-type or n-type dopant, each as described above.

The low-k precursor 1602 may be formed to any suitable thickness usingany suitable deposition technique (e.g., CVD, HDP-CVD, ALD, etc.). Insome examples, the low-k precursor 1602 has a thickness between about 1nm and about 10 nm and is deposited by conformal CVD and/or ALD process.The dopant may be introduced during deposition of the low-k precursor1602 via an in situ doping process. Additionally or in the alternative,the dopant may be introduced after the low-k precursor 1602 has beendeposited using an implantation process (e.g., ion implantation) toimplant the dopant.

Referring to block 1408 of FIG. 14A, an etching process is performed onthe workpiece 1500 to create recesses in which to form source/drainregions. This may be performed substantially as described in block 108of FIG. 1A.

Referring to block 1410 of FIG. 14A and to FIG. 17, an epitaxy processis performed on the workpiece 1500 to grow source/drain regions 602within the recesses. This may be performed substantially as described inblock 110 of FIG. 1A. A dopant activation process may be performed toactivate dopants within the source/drain regions 602, such as RTA and/ora laser annealing processes as shown in block 1412 of FIG. 14A. This maybe performed substantially as described in block 112 of FIG. 1A. In someexamples, the annealing process also activates the dopant within thelow-k precursor 1602 to form a low-k spacer layer 1702. Additionally orin the alternative, a separate dopant activation process may beperformed to activate the dopant within the low-k precursor 1602 to formthe low-k spacer layer 1702 as described in more detail below.

Referring to block 1414 of FIG. 14A and referring still to FIG. 17, aCESL 702 is formed on the workpiece 1500. Referring to block 1416 ofFIG. 14A, a first ILD layer 704 is formed on the workpiece 1500.Referring to block 1418 of FIG. 14B and to FIG. 18, a CMP process isperformed on the workpiece 1500. Referring to block 1420 of FIG. 14B andto FIG. 19, in examples where any components of the gate stack 204 areplaceholders, the placeholder components (such as the gate dielectric208 and/or the gate electrode 210) are removed as part of a gatereplacement process, leaving a recess 902 within the gate stack 204.These processes may be performed substantially as described in blocks114-120 of FIGS. 1A and 1B.

Referring to block 1422 of FIG. 14B, a dopant activation process isperformed on the workpiece 1500 to activate the dopant to form the low-kspacer layer 1702 when the annealing process of block 1412 is notsufficient. In various examples, the dopant activation process mayinclude RTA and/or a laser annealing to heat the workpiece 1500 to atemperature between about 450° C. and about 1050° C. The annealing maybe performed for second (or even fractions thereof) using ultrasub-second annealing (uSSA), spike annealing, laser annealing and otherrapid annealing techniques; may be performed for hours using furnaceannealing; or may be performed for any duration therebetween.

For examples where the low-k precursor 1602 includes a dielectricmaterial precursor and a porogen, a curing process is performed on theworkpiece 1500 in block 1424 to convert the low-k precursor 1602 intothe low-k spacer layer 1702. This may be performed substantially asdescribed in block 122 of FIG. 1B. The curing process is configured toconvert the dielectric material precursor of the low-k precursor 1602into a low-k dielectric material, and may drive off the porogen or causethe porogen to organize the molecular structure of the precursor tocreate voids in the low-k precursor 1602 without driving off theporogen. In various examples, the curing process applies radiation,heat, and/or inert or reactive gasses to cure the low-k precursor 1602and may be performed as part of and concurrent with the dopantactivation of block 1422 or separately therefrom. The dopant and/or thevoids created by the porogen may reduce the dielectric constant of thelow-k precursor 1602 to any suitable value, and in various examples, thelow-k spacer layer 1702 has a dielectric constant between about 3.9 andabout 1. In one such example, the low-k spacer layer 1702 has adielectric constant of about 3.

Referring to block 1426 of FIG. 14B and to FIG. 20, replacement elementsof the gate stack 204, such as a replacement gate dielectric 1002 and/ora replacement gate electrode 1004, are formed on the workpiece 200within the recess 902. This may be performed substantially as describedin block 124 of FIG. 1B.

Referring to block 1428 of FIG. 14B and referring still to FIG. 20, asecond ILD layer 1102 may be formed on the workpiece 1500. Referring toblock 1430 of FIG. 14B and to FIG. 21, a contact-open etching isperformed on the workpiece 1500 to form recesses that expose thesource/drain regions 602 where contacts are to be formed. Referring toblock 1432 of FIG. 14B and to FIG. 22A, the source/drain contact 1302 isformed on the workpiece 1500 within the recesses. These processes may beperformed substantially as described in blocks 126-130 of FIG. 1B.

The contact 1302 may extend between the vertical portions of the CESL702 and the sidewall spacer 304 such that the CESL 702 and the sidewallspacer 304 separate the contact 1302 from the adjacent gate stack(s)204. The structure and composition of the low-k spacer layer 1702 mayact to reduce this gate-contact capacitance. In particular, the dopeddielectric material of the low-k spacer layer 1702 formed in block 1406and the dopant activation of blocks 1412 and/or 1422 reduces thiscapacitance compared to other configurations. In some such examples, thelow-k spacer layer 1702 includes a porous low-k dielectric material inwhich the dopant is deposited that further acts to reduce thegate-contact capacitance.

Referring now to FIG. 22B, the inner spacer layer 302, the low-k spacerlayer 1702, the CESL 702, the gate stack 204, and the surroundingstructures of the workpiece 200 are enlarged for greater detail.Individual elements of the replacement gate electrode 1004 are shown,and in various examples, the replacement gate electrode 1004 includes acapping layer 1304, a barrier layer 1306, one or more work functionlayer(s) 1308 and/or an electrode fill 1310, each substantially asdescribed above.

As noted above, in various examples, the inner spacer layer 302 has awidth 1312 between about 1 nm and about 10 nm, the low-k spacer layer1702 has a width 1314 between about 1 nm and about 10, and the CESL 702has a width 1316 between about 1 nm and about 10 nm. The height 1318 ofthe gate stack 204 disposed between these layers (and by extension theheight of the inner spacer layer 302 and the CESL 702) is between about15 nm and about 25 nm in various examples. Accordingly a ratio of heightto width for the inner spacer layer 302 and CESL 702 may be betweenabout 1.5:1 and about 25:1. As the inner spacer layer 302 may extendbetween the low-k spacer layer 1702 and the substrate 202, the height ofthe low-k spacer layer 1702 is between about 5 nm and about 25 nm for acorresponding height-to-width ratio of between 0.5:1 and about 25:1 invarious examples.

Referring to block 1434 of FIG. 14B, the workpiece 1500 is provided forfurther fabrication.

Thus, the present disclosure provides examples of an integrated circuitwith a sidewall spacer and a technique for forming an integrated circuitwith such a spacer. In some examples, a method includes receiving aworkpiece that includes a substrate and a gate stack disposed upon thesubstrate. A spacer is formed on a side surface of the gate stack thatincludes a spacer layer with a low-k dielectric material. A source/drainregion is formed in the substrate; and a source/drain contact is formedcoupled to the source/drain region such that the spacer layer of thespacer is disposed between the source/drain contact and the gate stack.In some such examples, the low-k dielectric material includes a porouslow-k dielectric material. In some such examples, the forming of thespacer includes depositing a low-k dielectric material precursor and aporogen and curing the low-k dielectric material precursor to form thelow-k dielectric material of the spacer layer. The curing causes theporogen to create voids in the porous low-k dielectric material. In somesuch examples, the received gate stack includes a placeholder gateelectrode and the curing of the low-k dielectric material precursor isperformed after removing the placeholder gate electrode and beforeforming a functional gate electrode of the gate stack. In some suchexamples, the curing of the low-k dielectric material precursor includesapplying ultra-violet radiation to the workpiece. In some such examples,the forming of the spacer includes forming a hard mask layer directly onthe side surface of the gate stack and forming the spacer layer directlyon the hard mask layer. In some such examples, the low-k dielectricmaterial includes a dielectric material and a dopant from a groupconsisting of an n-type dopant and a p-type dopant. In some suchexamples, the forming of the spacer includes depositing the dielectricmaterial on the gate stack and in situ implanting the dopant during thedepositing of the dielectric material. In some such examples, theforming of the spacer includes depositing the dielectric material on thegate stack and thereafter performing an ion implantation process uponthe workpiece to implant the dopant within the dielectric material.

In further examples, a method includes receiving a substrate and a gatestack disposed on the substrate. A sidewall spacer is formed on avertical side surface of the gate stack. The sidewall spacer includes aspacer layer that includes a low-k dielectric precursor. The low-kdielectric precursor is cured to form a low-k dielectric material of thespacer layer. The curing forms a void within the low-k dielectricmaterial. A source/drain contact is formed adjacent the gate stack suchthat the sidewall spacer is disposed between the source/drain contactand the gate stack. In some such examples, the curing of the low-kdielectric precursor includes applying ultraviolet radiation to thespacer layer. In some such examples, the received gate stack includes aplaceholder gate electrode. The method further includes removing theplaceholder gate electrode and forming a functional gate electrode ofthe gate stack, and the curing of the low-k dielectric precursor isperformed after the removing of the placeholder gate electrode and priorto the forming of the functional gate electrode. In some such examples,the curing of the low-k dielectric precursor removes a porogen from thespacer layer to form the void within the low-k dielectric material. Insome such examples, the curing of the low-k dielectric precursor causesa porogen of the spacer layer to form the void within the low-kdielectric material, and the porogen remains within the spacer layerafter the curing. In some such examples, a hard mask layer of thesidewall spacer is formed directly on the vertical side surface of thegate stack, and the spacer layer is disposed directly on the hard masklayer. In some such examples, a contact etch-stop layer is formeddirectly on the spacer layer, wherein the contact etch-stop layerphysically contacts the source/drain contact.

In further examples, a device includes a substrate, a gate stackdisposed on the substrate, a sidewall spacer disposed on a side surfaceof the gate stack, and a source/drain contact disposed such that thesidewall spacer is disposed between the source/drain contact and thegate stack. The sidewall spacer includes a spacer layer with a low-kdielectric material, and the low-k dielectric material includes a voidtherein. In some such examples, the sidewall spacer includes a hard masklayer disposed between the spacer layer and the side surface of the gatestack. In some such examples, the device includes a contact etch-stoplayer disposed between the source/drain contact and the spacer layer. Insome such examples, the device includes a source/drain region to whichthe source/drain contact is coupled, and a vertical surface of thesource/drain region is aligned with a vertical surface of the sidewallspacer.

In further examples, a method includes receiving a workpiece thatincludes a substrate and a gate stack of a transistor disposed upon thesubstrate. A dielectric spacer is formed on a sidewall of the gatestack. The dielectric spacer includes a dielectric material doped with adopant. A source/drain contact of the transistor is formed on thesubstrate such that the dielectric spacer is disposed between thesource/drain contact and the gate stack. In some such examples, thedopant is from a group consisting of an n-type dopant and a p-typedopant. In some such examples, the dopant is from a group consisting ofboron and phosphorus. In some such examples, the forming of thedielectric spacer includes depositing the dielectric material and insitu doping the dielectric material with the dopant during thedepositing. In some such examples, the forming of the dielectric spacerincludes depositing the dielectric material and performing an ionimplantation on the dielectric material to implant the dopant. In somesuch examples, a dopant activation process is performed on thedielectric material and the dopant of the dielectric spacer. In somesuch examples, the dopant activation process is performed concurrentwith a source/drain dopant activation process of a source/drain regiondisposed in the substrate. In some such examples, the received gatestack includes a placeholder gate electrode, and the dopant activationprocess is performed after removing the placeholder gate electrode andbefore forming a functional gate electrode of the gate stack. In somesuch examples, the forming of the dielectric spacer forms the dielectricspacer to include a porogen, and the dopant activation process isperformed concurrent with a curing process that causes the porogen toleave a void within the dielectric spacer.

In further examples, a method includes receiving a substrate and a gatestack disposed upon the substrate. A hard mask layer of a sidewallspacer is formed on a side surface of the gate stack. A spacer layer ofthe sidewall spacer is formed on the hard mask layer. The spacer layerincludes a dielectric material and a dopant. A source/drain region isformed in the substrate adjacent the gate stack. A source/drain contactis formed coupled to the source/drain region such that the sidewallspacer is disposed between the source/drain contact and the gate stack.In some such examples, the dopant is from a group consisting of ann-type dopant and a p-type dopant. In some such examples, the dielectricmaterial is from a group consisting of: silicon oxide, silicon nitride,and silicon oxynitride. In some such examples, a dopant activationprocess is performed on the spacer layer and on the source/drain regionconcurrently. In some such examples, the received gate stack includes aplaceholder gate electrode, and the placeholder gate electrode isremoved from the gate stack. A functional gate electrode of the gatestack is formed, and a dopant activation process is performed on thespacer layer after the removing of the placeholder gate electrode andprior to the forming of the functional gate electrode. In some suchexamples, the forming of the spacer layer includes in situ doping of thedielectric material with the dopant during deposition of the dielectricmaterial.

In yet further examples, the device includes a substrate, a gate stackdisposed on the substrate, a sidewall spacer disposed alongside the gatestack that includes a dielectric material and a dopant, and asource/drain contact disposed alongside the sidewall spacer opposite thegate stack. In some such examples, the dopant is from a group consistingof an n-type dopant and a p-type dopant. In some such examples, thedielectric material is from a group consisting of: silicon oxide,silicon nitride, and silicon oxynitride. In some such examples, thedielectric material and the dopant are contained within a first layer ofthe sidewall spacer, and the sidewall spacer further includes a hardmask layer disposed between the first layer of the sidewall spacer andthe gate stack. In some such examples, a first portion of the hard masklayer is disposed between the first layer and the gate stack, and asecond portion of the hard mask layer is disposed between the firstlayer and the substrate.

The foregoing outlines features of several examples so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the examples introduced herein. Thoseskilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device comprising: a gate stack disposed on asubstrate; and a first sidewall spacer formed of a low-k dielectricmaterial and disposed on the gate stack, wherein the low-k dielectricmaterial includes a porous low-k dielectric material and a dopantselected from the group consisting of a first-type dopant and asecond-type dopant, the second-type being opposite the first-type. 2.The device of claim 1, wherein the wherein the low-k dielectric materialhas a dielectric constant of about
 3. 3. The device of claim 1, whereinthe low-k dielectric material is a material having a dielectric constantof 1 to less than 3.9.
 4. The device of claim 1, wherein the dopantselected is the first-type dopant which is a p-type dopant.
 5. Thedevice of claim 1, wherein the dopant selected is the second-type dopantwhich is an n-type dopant.
 6. The device of claim 1, further comprisinga source/drain feature disposed on the substrate and associated with thegate stack, the source/drain feature including the first-type dopant andthe low-k dielectric material including the second-type dopant.
 7. Thedevice of claim 1, further comprising a second sidewall spacer disposeddirectly on the gate stack between the gate stack and the first sidewallspacer, wherein the second sidewall spacer prevents the first sidewallspacer from interfacing with the gate stack.
 8. The device of claim 7,wherein the gate stack includes: a gate dielectric layer interfacingwith the second sidewall spacer; a capping layer disposed on the gatedielectric layer; a barrier layer disposed on the capping layer; a workfunction metal layer disposed on the barrier layer; and a metal filllayer disposed on the work function metal layer.
 9. A device comprisinga first gate stack disposed on a substrate; a first sidewall spacerdisposed along and interfacing with the first gate stack; and a secondsidewall spacer formed of a low-k dielectric material and disposed alongand interfacing with the first sidewall spacer, wherein the low-kdielectric material includes a dielectric material and a dopant selectedfrom the group consisting of an n-type dopant and a p-type dopant,wherein the low-k dielectric material has at least one void therein. 10.The device of claim 9, further comprising an etch stop layer disposeddirectly on the second sidewall spacer.
 11. The device of claim 10,further comprising: a source/drain feature dispose on the substrate; acontact extending to the source/drain feature; and wherein the etch stoplayer extends from the second sidewall spacer to the contact such thatthe etch stop layer prevents the second sidewall spacer from interfacingthe contact.
 12. The device of claim 10, wherein a top surface of thefirst sidewall spacer, a top surface of the second sidewall surface anda top surface of the etch stop layer form a planarized surface facingaway from the substrate.
 13. The device of claim 9, wherein thedielectric material includes a material selected from the groupconsisting of a semiconductor oxide, a semiconductor nitride, asemiconductor oxynitride, a semiconductor carbide, and a semiconductoroxycarbonitride.
 14. The device of claim 9, wherein the low-k dielectricmaterial is a material having a dielectric constant of 1 to less than3.9.
 15. The device of claim 9, further comprising: a source/drainfeature disposed on the substrate; and a contact extending to thesource/drain feature, a second gate stack disposed on the substrate; athird sidewall spacer formed of the low-k dielectric material anddisposed on the second gate stack, the third sidewall spacer having asidewall surface facing the contact and the second sidewall spacerhaving a sidewall surface facing the contact; an etch stop layerincluding a first portion disposed along and interfacing with the entiresidewall surface of the third sidewall spacer and a second portiondisposed along and interfacing with the entire sidewall surface of thefirst sidewall spacer.
 16. A device comprising: a gate stack disposed ona substrate, the gate stack including a u-shaped gate dielectric layerand a fill material at least partially surrounding by the u-shaped gatedielectric layer; a first sidewall spacer disposed on a side surface ofthe gate stack, wherein the first sidewall spacer is formed of a porouslow-k dielectric material; and a second sidewall spacer disposed betweenthe first sidewall spacer and the gate stack such that the secondsidewall spacer interfaces with the u-shaped gate dielectric layer ofthe gate stack.
 17. The device of claim 16, wherein the second sidewallspacer interfaces with the first sidewall spacer and extends underneaththe first sidewall spacer.
 18. The device of claim 16, wherein theporous low-k dielectric material includes a dopant.
 19. The device ofclaim 16, wherein the porous low-k dielectric material has a dielectricconstant of less than silicon nitride to at least
 1. 20. The device ofclaim 16, wherein a top surface of the u-shaped gate dielectric layer, atop surface of the first sidewall spacer and a top surface of the secondsidewall spacer each extend to the same height above the substrate, therespective top surfaces of the u-shaped gate dielectric layer, the firstsidewall spacer and the second sidewall spacer facing away from thesubstrate.